Water-insoluble aqueous emulsion copolymers of monoethylenically unsaturated monomers including a significant proportion of copolymerized carboxyl-functional monomer so that they swell or dissolve in water upon the addition of alkaline material are known. These copolymerized monomers produce anionic copolymer thickeners useful in ordinary aqueous latex paints because of the presence in the copolymer of large amounts of copolymerized carboxyl-functional monomer together with copolymerized monomer having surfactant character. This is taught in U.S. Pat. No. 4,384,096 issued May 17, 1983 which uses an acrylate ester monomer as the surfactant monomer. This is also taught using a urethane monomer as the surfactant monomer to obtain a better balance of low shear and high shear properties in G. D. Shay, E. Eldridge and J. E. Kail U.S. Pat. No. 4,514,552 issued to the assignee of this application on Apr. 30, 1985.
In this U.S. Pat. No. 4,514,552, the surfactant monomer is provided by the reaction product of a monoethylenically unsaturated monoisocyanate with a monohydric surfactant which is normally a polyethoxylated hydrophobe, as is conventional in the surfactant art. The polyethoxylation is usually carried out using ethylene oxide, but surfactants can also be made when a portion of the ethylene oxide is replaced by propylene oxide, and this is also disclosed in U.S. Pat. No. 4,514,552. However, when the ethylene oxide is completely replaced by propylene oxide, butylene oxide, or a mixture thereof, the conventional surfactant characteristics are no longer present because the monomers are entirely hydrophobic.
The alkali-soluble aqueous emulsion copolymers disclosed in U.S. Pat. No. 4,514,552 are especially useful in providing thickeners for ordinary aqueous latex paints having the previously noted better balance of low shear and high shear properties, and this is especially important in semi-gloss paints and gloss paints. However, when the ethylene oxide is completely replaced by propylene oxide, butylene oxide, or a mixture thereof, the products are no longer useful in ordinary aqueous latex paints to provide desirable viscosity characteristics for leveling and brush drag since they do not provide useful rheology for such purpose. As discovered in the present invention, use of a polypropoxylated and/or polybutoxylated nonionic monomer unexpectedly provides improved anti-settling and improved anti-sag properties.
More particularly, preferred emulsion copolymers in accordance with U.S. Pat. No. 4,514,552 contain 30% ethyl acrylate, 35% methacrylic acid and 35% of urethane-based surfactant monomer in which the surfactant portion of the molecule is a polyethoxylated monohydric hydrophobe, such as an octyl or nonyl phenol. These thickeners provide a reasonably good balance of low shear viscosity needed for leveling and high shear viscosity needed for brush drag when incorporated into aqueous latex paints which are alkaline to dissolve the copolymer. While these viscosities are reasonably good, the low shear viscosity is still too low and the high shear viscosity is still too high, and efforts have been made to correct this. On the other hand, typical emulsion copolymers contemplated by the invention discussed herein provide low shear viscosities which are still lower and high shear viscosities which are still higher than those obtained in the patent under consideration, and this makes these products far less useful in ordinary latex paints for the purpose of adjusting these viscosities.
On the other hand, there are several utilities for the thickeners of this invention described hereinafter in which thickening characteristics very different from those needed in ordinary latex paints are essential. To illustrate these, anti-settling characteristics are important in aqueous agricultural emulsions and dispersions, as well as in aqueous cosmetic compositions and aqueous oil field drilling compositions.
Even some paints require unusual rheological characteristics, such as textured paints which are applied with a large napped roller so as to deposit a configured layer. It is desired to retain this configuration as the paint dries, and this is the opposite of the usually desired flow which eliminates brush marks and roller marks.
In addition, some conventional paints have too much brush drag (i.e., are hard to apply) and/or too much leveling which causes sagging. The thickeners of this invention can be added in a minor proportion of total thickener to correct the rheology and also provide improved anti-settling and anti-sag properties.